1. Field of the Invention
This invention relates to improvements in double cylinder deadbolts and particularly to a double cylinder deadbolt in which the inside key is retained but can be released only through operation of the outside lock.
2. Description of the Prior Art
Double cylinder lock deadbolts have become important security mechanisms and are recommended by police and security advisors for both residence and commercial applications. A double cylinder lock deadbolt is a deadbolt which may be installed in a door and slidably projected to a stationary keeper with two locking cylinders one on each side of the door. Either of these locking cylinders may be utilized to lock or unlock the deadbolt. The use of two cylinders creates the effect of a double barrier. For maximum security double cylinder deadbolts are recommended even against the burglar who gains entry through a window as then he cannot get out the door because he cannot unlock the door from the inside unless he has the key to the inside cylinder. This eliminates doors as an escape route and also eliminates to some extent the size and weight of the articles which may be stolen and transported as they must be taken back out the path of entry.
Even with the security advantages of double cylinder lock deadbolts, however, there are disadvantages with regard to fire safety which have caused some concern. A number of states have enacted laws which prevent locksmiths from installing double cylinder deadbolts due to fire or panic danger. This danger results if the inside cylinder lock key is removed and not readily available in the case fire or panic preventing exit convenience. Apparently, this fire or panic safety problem was the reason for the state laws prohibiting locksmiths from installing double cylinder deadbolts.
The problem of security on one hand and fire safety on the other hand in connection with double cylinder deadbolts has previously been addressed in my prior patent application, Ser. No. 19,024 filed Mar. 8, 1979 and now abandoned. In that invention, I utilized the concept of a removable key/thumbturn. Even though the invention of that application has been a significant commercial success, it still does not meet some of the objections from a fire safety standpoint in that the inside key might be removed inadvertently thus barring exit in the case of fire or panic. However, if the inside key can be positively retained by a lock and only removed when the outside key is in the lock and is actuated to release the inside key. This would allow the inside key to be removed only when the possessor of the outside key purposely desires to do so, e.g., when leaving a home for vacation or the like. This alleviates the fire and panic danger objection to the usual double cylinder deadbolt because one canot inadvertently or surrepticiously remove the inside key.
Another known double cylinder deadbolt with a safety feature is shown in U.S. Pat. No. 4,068,510, granted Jan. 17, 1978. This patent also provides an arrangement in which the inside key is retained or held but it is retained or held only when the bolt is projected, i.e., when the door is locked. If the door is unlocked, the inside key can be removed. If a double cylinder deadbolt is used in a store or the like where the door is unlocked during working hours, someone can inadvertently remove the inside key when the door is open and then lock the door at the end of the day possibly locking someone in the store without their knowledge. In that case the person in the store has no means of exit.
Accordingly, this invention provides a unique arrangement for retaining the inside key under control of the outside locking cylinder so that the inside key may be retained unless the holder of the outside key purposely unlocks it and remove the inside key.